This invention relates to an electronic apparatus having a vibration-sensitive constructional unit accommodated in a housing, the housing and the vibration-sensitive constructional unit being coupled by damping means.
Such an electronic unit is known, for example, from DE 39 14 303 A1. This known apparatus uses helical springs with a linear spring-force characteristic in order to provide isolation from external vibrations and shocks between the apparatus chassis or deck and the mounting structure or housing of the apparatus. The vibration amplitude of such helical springs for excitation by vibrations of comparatively low frequency is larger than for excitation by vibrations of comparatively high frequency. In such apparatuses the vibration clearance for the vibration-sensitive constructional unit should therefore be adapted to the lowest excitation frequencies that occur in operation.
It is an object of the invention to provide an apparatus of the type defined in the opening paragraph, wherein the vibration clearance required for the vibration-sensitive constructional unit is reduced.
According to the invention this object is achieved in that the damping means comprise at least one spring arrangement having a spring characteristic which is progressive in three directions in space.
In the usual case, the length of a compressed spring is shortened proportionally to the force which is applied to the spring e.g. if the force is doubled the length of the spring is halved. According to Applicants"" invention, a progressive spring characteristic results in a spring that is shortened other than proportionally, e.g. if the compressive force is doubled the length of the spring is not reduced in half, for example, less than half.
A progressive spring characteristic means that the spring force increases progressively as the vibration amplitude or spring travel increases. When a spring vibrates, the difference between the shortest and the longest extension of the spring is called vibration amplitude. The spring characteristic, which is progressive in three directions in space, results in a progressive damping of vibrations in all three directions in space. The three directions in space are defined as directions in space of a Cartesian coordinate system. One axis of this Cartesian coordinate system is then preferably oriented in the direction of the longitudinal axis of the spring arrangement. Thus, vibrations that occur are damped progressively in three dimensions.
The vibration amplitude of the low-frequency vibrations is reduced as a result of the nonlinear tuning of the springs with progressive spring characteristics. This results in a reduction of the vibration clearance required for the vibration-sensitive constructional unit in all three directions in space and, consequently, of the construction volume of the electronic apparatus in all three directions in space.
In one advantageous embodiment of the invention the spring arrangement comprises a helical spring with non-linearly spaced turns. This non-linear spacing results in a non-linear spring characteristic of the helical spring which is progressive in the axial direction of the helical spring. A spring core is arranged inside the helical spring and the radial clearance between the turns of the helical spring and the spring core is not constant. Thus, it is achieved that as the vibration amplitude increases an increasing number of turns of the helical spring come into contact with the spring core, as a result of which the vibrations are damped progressively with increasing vibration amplitude and a spring characteristic is obtained which is progressive in space directions which extend radially with respect to the helical spring. Preferably, the spring core comprises a tapered non-elastic body.
In another advantageous embodiment of the invention the spring core is fixedly connected to the housing. The radial clearance between the turns of the helical spring and the spring core increases from the housing towards the vibration-sensitive constructional unit, i.e. near the housing the clearance between the turns of the helical spring and the spring core is comparatively small, while near the vibration-sensitive constructional unit it is comparatively large. Therefore, when the vibration-sensitive constructional unit is subjected to vibrations the helical spring, as the vibration amplitude increases, first comes into contact with the part of the spring core situated near the housing. When the vibration amplitude increases further an increasing number of turns of the helical spring come into contact with the spring core, which results in a spring characteristic which is progressive in space directions oriented radially with respect to the helical spring and, consequently, in a progressive damping of the vibration amplitude.
In a further advantageous embodiment the spring core is connected to the vibration-sensitive constructional unit and, consequently, vibrates along with the vibration-sensitive constructional unit. The radial clearance between the turns of the helical spring and the spring core in the present embodiment decreases from the housing towards the vibration-sensitive constructional unit, i.e. near the vibration-sensitive constructional unit the clearance between the turns of the helical spring and the spring core is comparatively small, while it is comparatively large near the housing. Therefore, when the vibration-sensitive constructional unit is subjected to vibrations and the vibration amplitude increases, only the turns of the helical spring situated near the vibration-sensitive constructional unit come initially into contact with the spring core. When the vibration amplitude increases further an increasing number of turns of the helical spring come into contact with the spring core, which results in a spring characteristic which is progressive in a radial direction and, consequently, in a progressive damping of the vibration amplitudes of the vibration-sensitive constructional unit.
The embodiments of the electronic apparatus in accordance with the invention are suitable for use in apparatuses for playing back or inscribing optical storage discs, such as for example CDs or DVDs. The electronic apparatus in accordance with the invention is particularly suitable for mounting in motor vehicles because the mounting room in motor vehicles is limited and numerous vibrations of different frequencies occur during the ride.